Cephalopelvic Disproportion (CPD) is a condition where the baby’s head or body does not fit through the mother’s pelvis. This can happen when the baby is too big, the pelvis is too small, the baby is in a wrong position, or the relationship between the baby and the pelvis is incorrect even though the baby is not too big and the pelvis is not too small.
CPD is often diagnosed when a woman’s labor fails to progress to delivery, the cervix has stopped to dilate, or the baby does not descend through the pelvis. In cases of actual CPD, a cesarean section (C-section) is usually indicated
CPD may be the result of a large baby (macrosomia). A baby may be larger than normal because of hereditary factors, diabetes, or postmaturity, which is a pregnancy that extends past the due date. There is no strict cutoff for the definition of macrosomia, and many consider a baby over 4,000 grams to have macrosomia, while others have a cutoff of 4,500 grams. Babies of mothers with diabetes are considered too big at a lower weight because their abdomen is usually out of proportion. Babies born to mothers who have had other children are more likely to be large. Other causes of CPD include abnormal fetal positions and a mother with a small or abnormally shaped pelvis.
A doctor will diagnose cephalopelvic disproportion when labor does not move along as swiftly as it should, with adequate contractions and even with the use of oxytocin or other medical therapies to speed labor. The medical staff will say there is a lack of progress in labor if the mother’s cervix is not dilating or the baby’s head is not descending down the birth canal as it should.
Though macrosomia can be diagnosed before labor, the physician cannot diagnose CPD before labor begins, even if the baby’s head or body appears unusually large or he worries the mother’s pelvis will be too small; the mother’s pelvic joints spread during labor and the baby’s head molds to the shape of the birth canal. The doctor may use ultrasound to measure the baby’s size but must rely on a physical examination to determine pelvis size. There is not a good reliability of diagnosing macrosomia with ultrasound. Many physicians would choose to perform a cesarean section (C-section) on larger babies.
Complications of CPD include an increased risk of cesarean section and shoulder dystocia with a vaginal delivery as well as an increased risk of postpartum bleeding.
Most women with CPD have a successful pregnancy outcome after a cesarean delivery and there is no evidence to suggest that CPD affects a baby after its birth. Statistics suggest that about one out of 3 cesarean sections are the result of some form of CPD. Another study shows that 65 percent of women who received a diagnosis of cephalopelvic disproportion in an earlier pregnancy went on to deliver vaginally in subsequent pregnancies. In fact, many of these women had larger babies on subsequent pregnancies than with the CPD baby.